This invention relates to the art of image recording apparatus of a type that performs image recording on the basis of image data (image information) as received from its external supply source.
Scanned image recording is utilized in various applications including printers and copiers. In scanned image recording, means of recording which performs image recording in only one direction (main scanning direction) is moved relative to a recording material in an auxiliary scanning direction which is perpendicular to the main scanning direction, whereby an image is recorded two-dimensionally on the recording material.
For example, thermal image recording involves the use of a thermal head having a glaze in which heat-generating elements for heating the thermal recording layer of a thermal recording material to record an image are arranged in one direction (main scanning direction) and, the thermal head and the thermal material are relatively moved in the auxiliary scanning direction perpendicular to the direction in which the glaze extends, by scanning and transporting the thermal material or the thermal head with the glaze a little pressed against the thermal material (thermal recording layer), and the respective heat-generating elements of the glaze are heated imagewise by energy application to heat the thermal recording layer of the thermal material, thereby accomplishing image reproduction.
This thermal image recording is commonly used to record images produced in diagnosis by ultrasonic scanning. This recording method eliminates the need for wet processing and offers several advantages including convenience in handling. Hence in recent years, the use of the thermal image recording system is not limited to small-scale applications such as diagnosis by ultrasonic scanning and an extension to those areas of medical diagnoses such as CT, MRI and X-ray photography where large and high-quality images are required is under review.
In scanned image recording by means of optical beams, an optical beam modulated in accordance with the image to be recorded is deflected in the main scanning direction while the light-sensitive material is transported in the auxiliary scanning direction. In scanned image recording using an LED array, the LED array and the light-sensitive material are moved relative to each other in a direction perpendicular to the direction in which the individual LEDs are arranged and, at the same time, the luminous elements (pixels) in the LED array are activated in accordance with the image to be recorded. Thus, in above both cases, the light-sensitive material is scan exposed two-dimensionally to perform image recording.
These types of scanned image recording have a common problem in that even if it is attempted to perform image recording at uniform density, individual recording apparatus have their own peculiar characteristics which cause uneven image densities in the main scanning direction. This phenomenon is commonly called "shading" and deteriorates the quality of the recorded image.
In the case of thermal image recording, the shape of the glaze on the thermal head is not uniform throughout all pixels but scatters unavoidably; therefore, even if the respective heat-generating elements are supplied with the same amount of energy, they will generate different amounts of heat, causing "shading" or unevenness in the density of the image being recorded.
In order to prevent the deterioration in image quality due to "shading", certain models of image recording apparatus are adapted to perform "shading compensation", in which the unevenness in image density due to shading is corrected. A typical procedure of shading compensation is as follows. First, image recording is performed on the basis of image data having uniform density in the main scanning direction; the densities of the recorded image are measured and with a certain pixel, say, one of a minimal density, being taken as a reference, the coefficient of shading compensation which will provide a uniform image density for all pixels is calculated for each pixel and stored in a suitable device such as a memory (this is a step of setting the conditions for shading compensation). With the conditions for shading compensation having been thusly set, shading compensation in actual image recording is performed by multiplying the image data from its supply source by the calculated coefficients of shading compensation.
However, the state of shading varies with time and as the image recording apparatus is used continuously, the initial settings of the conditions for shading compensation are no longer capable of assuring the intended results but the quality of the recorded image will deteriorate gradually. In the case of thermal image recording, the glaze (or its protective layer) deteriorates by wear in the course of image recording and, in addition, stain is deposited on the glaze, whereby the amount of heat generated in response to a given supply of energy will fluctuate over time. What is more, this fluctuation in heat generation differs from one pixel to another. As a result, the state of shading varies with time and the intended shading compensation can no longer be accomplished on the basis of the initially set conditions.
The deterioration in the quality of the recorded image due to such insufficient shading compensation is a serious problem in applications that require the recording of high-quality images. Particularly in the case of the aforementioned thermal recording apparatus for use in medical applications, the deteriorated image quality is an obstacle to the correct viewing of the image, potentially leading to an error in diagnosis.
In order to avoid these problems, the conditions for shading compensation must be updated depending on the state of deterioration in image quality and this is usually accomplished in one of the following ways: a serviceman visits the user and performs the necessary updating procedure; the user sends his apparatus to a service shop for updating; the user sends to a service shop the image he has recorded in a preliminary step of the aforementioned process of setting the conditions for shading compensation and a serviceman updates the settings of the conditions for shading compensation and records the updated conditions in a medium such as a floppy disk, which is sent back to the user who then downloads it. However, these procedures are a substantial burden on both the user and the serviceman.